Diamond Bar

One ADU is permitted on each residentially zoned lot and may be attached, detached, or created within an existing primary dwelling. The ADU must include independent living facilities such as a kitchen, bathroom and sleeping area.

One JADU is permitted on single-family residential lots and must be located within the walls of the primary residence. The JADU may share sanitation facilities with the main home and must include a basic kitchen.

Diamond Bar follows California state ADU laws and provides additional local standards under its municipal code, with programs to streamline approvals.

• Detached ADU: A standalone residential unit located on the same lot as the primary home
• Attached ADU: A unit that is physically connected to the main house
• Conversion ADU: A unit created within existing space such as a garage, attic, or interior portion of the home
• Junior ADU (JADU): A unit up to 500 sq. ft. within the primary residence, with a basic kitchen and optional shared bathroom

• Maximum Size:
  
  • Detached: 
    
    • Up to 850 sq. ft. for studio or one-bedroom units
    • Up to 1,000 sq. ft. for units with two or more bedrooms
      

• Setbacks:
  
  • Must comply with local development standards and building code requirements (referenced under municipal code)
    
    
• Height Limits:
  
  • Subject to zoning and development standards under the City’s Development Code

• Parking Requirements:
  
  • Parking requirements follow state law and city development standards
  • Specific requirements depend on project conditions and location

To build an ADU in Diamond Bar, the following approvals and submittals are typically required:

• Initial planning inquiry submission
• Preparation of architectural and site plans
• Review by Planning and Building & Safety Divisions
• Formal building permit application and plan check

Once submitted:

• Initial review for completeness takes a few days
• Plan check turnaround is approximately 15 working days per review cycle

ADU permit timelines in Diamond Bar follow California state law requiring timely processing of complete applications. The typical process includes an initial completeness review within a few days, followed by plan check cycles that generally take about 15 working days, with any subsequent corrections reviewed within approximately 10 working days. The final permit is issued once all required corrections have been addressed.

ADUs are permitted on all residentially zoned properties, regardless of lot size.

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Both ADUs and JADUs are allowed on single-family properties, subject to development standards and building code compliance.

For the most current and complete information, refer directly to the City of Diamond Bar.

Diamond Bar also offers a Pre-Approved ADU Program (DBADU), which provides standardized plans that meet city and state requirements and can help streamline the permitting process.

ADU regulations are constantly evolving and may vary by property. Before starting your project, it’s recommended to consult with a qualified professional or ADU specialist to ensure compliance with current local requirements.